"Unsubdivide" = Reduce vertices in loops
From MoonBoots' comment, Checker Deselect seems to be an effective solution. Ctrl+Alt+RMB over a perpendicular (non-loop) edge; Select -&gt; Checker Deselect; Select -&gt; Edge Loops; and delete edge loops. Under Checker Deselect, the N option determines deselect pattern (e.g. n=2 means -/+ and n=3 means -/-/+ if skip=1), and the Skip option determines number of adjacent edges to be included in that + (e.g. skip=2 means (+/+)/- and skip=3 means (+/+/+)/- if n=2). See video (does not demonstrate use of N and Skip options): https://www.youtube.com/watch?v=Yptda_yKQIU